package think.polymorphism;

class Useful{
    public void f(){}
    public void g(){}
}

class MoreUseful extends Useful{
    @Override
    public void f(){}
    @Override
    public void g(){}
    public void u(){}
    public void v(){}
    public void w(){}
}

public class RTTI {

    public static void main(String[] args) {
        Useful x[]={new Useful(),new MoreUseful()};
        x[0].f();
        x[1].g();

        //向下转型
        ((MoreUseful)x[1]).u();
        ((MoreUseful)x[0]).u();

    }

}
